Molecular cloning and functional characterization of apple U-box E3 ubiquitin ligase gene MdPUB29 reveals its involvement in salt tolerance

An E3 ubiquitin ligase gene (Genbank accession no.: MD01G1010900) was cloned from the Royal Gala apple genome (Malusxdomestica Borkh.). Sequence analysis showed that the length of the MdPUB29 gene was 1 275 bp, encoding 424 amino acids. Phylogenetic tree analysis indicated that the apple E3 ubiquitin ligase exhibited the greatest sequence similarity to Pyrus×bretschneideri. The predicted protein structural domain of MdPUB29 showed that it contained a U-box domain. qRT-PCR analysis showed that MdPUB29 was expressed widely in different tissues of the Royal Gala apple species, and was highly expressed in the root, while the expression of MdPUB29 was significantly inhibited by exogenous NaCl. Immunoblotting assays revealed that MdPUB29 protein abundance in tissue cultures of the Royal Gala apple accumulated under NaCl stress conditions. Three-dimensional protein structure prediction indicated that MdPUB29 was highly homologous with AtPUB29. The growing potential of MdPUB29-expressing apple calli and Arabidopsis were much stronger than that of the control under salt stress conditions, suggesting that MdPUB29 may positively regulate salt tolerance.